It would be just fine. Because once you reach a western style of living birth rates fall below replacement. See Western Europe, Japan and the US to a lesser extent for examples.
Less population and greater efficieny means less demand for fossil fuels and a dramatic drop in green house gases. Plus nobody has to live in the dark ages.
Dark ages based on your beliefs.
Anyway, how long will it take these countries to "Westernize?" 100 years? By then, what will the world's population be?
Currently, it is the opposite. I don't see China, India, Brazil and others becoming green by following the Western model. The West is supposedly becoming more green in one way but their per capita footprint will likely be higher than the developing world. Where is the green in that?
A family living in a mud house in Africa will not become any more greener by adopting a Western style of living. Of course, this is what is happening. The West, in many people's eyes, has a superior way of living and that is the current trend in the world.
Let's see what happens. I'm just talking so please don't take me too seriously.